This invention relates to high power factor conversion circuitry and more particularly to high power factor ballast circuitry especially suitable for use with flourescent lamps.
At present, the most common form of ballast circuit for flourescent lamps is the 60-Hz auto-transformer type of ballast. However, it is well known that such apparatus is both heavy and cumbersome which are undesirable features for a structure which is frequently mounted overhead. Moreover, it is known that such apparatus is relatively inefficient which causes generation of undesired heat and energy losses.
Another form of ballast circuit utilizes a flip-flop oscillator and a saturable core transformer. The oscillator saturates and, in turn, saturates the core of the transformer to limit current flow. Unfortunately, core saturation characteristics are difficult to accurately predict. Thus, reliability and predictability of such apparatus leaves much to be desired.
Still another form of ballast circuit is disclosed in the above-mentioned co-pending U.S. applications assigned to the Assignee of the present application. Therein, a sinusoidal wave from an AC potential source is rectified to provide a pulsating DC potential. This pulsating DC potential is applied to an oscillator circuit which provides a high frequency output potential which is coupled to a lamp circuit. The circuitry also includes circuitry to compensate for "storage time" of the transistor as well as circuitry for clamping the rectifier to inhibit a "runaway" condition upon removal of the lamp load.
Although the above-mentioned high frequency ballast circuitry provides enhanced capabilities unattainable in previously known apparatus, it has been found that an improved response without deleterious effect on the power factor of the circuitry is a most desirable feature. Also, a reduction in circuit complexity without a decrease in power factor would be most desirable.